Radio frequency identification (RFID) systems generally consist of at least one host reader and a plurality of transponders, which are commonly termed credentials. The transponder is an active or passive radio frequency communication device, which is directly attached to or embedded in an article to be identified or otherwise characterized by the reader, or which is alternatively embedded in a portable substrate, such as a card, keyfob, tag, or the like, carried by a person or an article to be identified or otherwise characterized by the reader.
A passive transponder is dependent on the host reader as its power supply. The host reader “excites” or powers up the passive transponder by transmitting high voltage excitation signals into the space surrounding the reader, which are received by the transponder when it is near, but not necessarily in contact with, the reader. The excitation signals from the reader provide the operating power for the circuitry of the recipient transponder. In contrast, an active transponder is not dependent on the reader as its power supply, but is instead powered up by its own internal power source, such as a battery. Once the transponder is powered up, the transponder communicates information, such as identity data or other characterizing data stored in the memory of the transponder, to the reader and the reader can likewise communicate information back to the transponder without the reader and transponder coming in contact with one another.
The powered up transponder communicates with the reader by generating transponder data signals within the circuitry of the transponder and transmitting the transponder data signals in the form of electromagnetic waves into the surrounding space occupied by the reader. The reader contains its own circuitry to “read” the data contained in the transponder data signals received from the transponder. Exemplary RFID systems communicating in this manner are disclosed in U.S. patents U.S. Pat. No. 4,730,188 to Milheiser (the '188 patent), U.S. Pat. No. 5,541,574 to Lowe et al. (the '574 patent), and U.S. Pat. No. 5,347,263 to Carroll et al. (the '263 patent), all of which are incorporated herein by reference.
RFID systems are generally characterized by a number of parameters relating to transmission and processing of the data signals. Such parameters include the carrier frequency of the data signals, the transfer rate of the data in the data signals, and the type of modulation of the data signals. In particular, data signals communicated between the transponder and reader of a given RFID system are usually at a specified standard carrier frequency, which is characteristic of the given RFID system. For example, RFID systems, which employ transponders of the type conventionally termed proximity cards or proximity tags, typically communicate by means of data signals at a carrier frequency within a range of 100 to 150 kHz. This carrier frequency range is nominally referred to herein as 125 kHz carrier frequency and is deemed a low frequency. In contrast, RFID systems, which employ transponders of the type conventionally termed smart cards, typically communicate by means of data signals at a higher frequency of 13.56 MHz.
The transfer rate of digital data communicated between the transponder and reader of a given RFID system via the data signals is commonly at one of a number of specified standard data rates, which is also characteristic of the given RFID system. The specified data rates are usually a function of the carrier frequency for the given RFID system. For example, RFID systems operating at the 125 kHz carrier frequency typically employ a relatively low data rate on the order of a few kilobits per second. For RFID systems operating at the 13.56 MHz carrier frequency, one particular industry standard specifies a low data rate of about 6 kilobits per second and a high data rate of about 26 kilobits per second. Another industry standard specifies an even higher data rate of 106 kilobits per second for RFID systems operating at the 13.56 MHz carrier frequency.
Finally, the type of modulation applied to data signals in a given RFID system is also characteristic of the given RFID system. Among the different modulation types available to RFID systems are frequency shift keying (FSK), phase shift keying (PSK) and amplitude shift keying (ASK).
As a rule, the circuitry of the reader is more extensive and complex than the circuitry of the transponder because the reader requires a higher degree of functionality relative to the transponder, particularly in the case of a passive transponder. Whereas most of the functionality of the transponder can normally be contained within a single integrated circuit, the diverse functionality of the reader typically requires a plurality of separate and discrete non-integrated (i.e., external) electronic components. For example, FIGS. 1–3 and 6 and the associated text of the '188 patent disclose separate specific hardware for generating an excitation signal transmitted into the surrounding space from a reader antenna which enables powering up of nearby passive transponders. The '188 patent also discloses separate specific hardware for detecting transponder data signals from among the signals received from the surrounding space on the reader antenna, for conditioning the transponder data signals received from the surrounding space when detected, and for demodulating the resulting conditioned transponder data signals, respectively, to read the data contained in the transponder signal.
The '263 patent refines the reader circuitry of the '188 patent by integrating certain electronic components of the reader circuitry of the '188 patent, such as decoders and drivers, into a single-chip microcontroller. In accordance with the '263 patent, operation of the reader comprises receiving a transponder data signal on the reader antenna and feeding the transponder data signal to a multi-stage band pass amplifier downstream of the reader antenna and upstream of the microcontroller. The multiple stages of the band pass amplifier condition, i.e., filter and amplify, the transponder data signal. The resulting conditioned transponder data signal is passed to the microcontroller where the data contained in the transponder data signal is read.
Although the design of the reader disclosed in the '263 patent realizes some economies of size and cost over the prior art by integrating a plurality of electronic components and their functionalities into the microcontroller of the reader, the use of an external multi-stage band pass amplifier limits the practicality of the reader for universal applications. In order to universally adapt the reader of the '263 patent to the multiplicity of different available carrier frequencies, data rates, and modulation types recited above, the reader would require a separate external multi-stage receiver for each variation of carrier frequency, data rate, and modulation type, respectively. It is readily apparent that a universal reader based on the reader design of the '263 patent would require many additional external receiver components, thereby offsetting any advantage gained by integrating other reader components and functionalities into the reader microcontroller.
The present invention disclosed hereafter recognizes the particular desirability of eliminating the external multi-stage band pass amplifier in the circuitry of the reader or at least reducing the number of stages of the band pass amplifier so that the reader more efficiently accommodates a range of carrier frequencies, data rates, and modulation types for signals received by the reader. The present invention also recognizes the desirability of integrating the functionalities of other electrical components into the microcontroller of the reader in addition to or in the alternative to those disclosed in the '263 patent. For example, the present invention recognizes the specific desirability of integrating power conservation functionalities into the microcontroller of the reader.
U.S. Pat. No. 6,476,708 to Johnson (the '708 patent) discloses a reader having relatively low power consumption requirements. Low power consumption is a particularly advantageous characteristic for a reader, which is powered by a self-contained portable power source within the reader, such as a small disposable or rechargeable battery. Use of the self-contained power source enables a user to position the reader in a remote location which lacks access to an ac power line or an ac power outlet. A battery, however, has a finite life necessitating replacement of the battery in the reader at the end of its useful life, which is both costly and time consuming. Accordingly, it is desirable to reduce the power demands on the battery during operation, thereby extending the useful life of the battery.
The reader of the '708 patent includes an excitation signal generator circuit, transponder detection circuit coupled to the excitation signal generator circuit, and a power source in the form of a small portable battery. The excitation signal generator circuit unit initially operates in a reduced power state effected by drawing reduced electrical current from the power source. The excitation signal generator circuit generates ring signals containing analog data in response to the reduced electrical current. The ring signals are transmitted from a reader antenna and the ring signals propagate into the space surrounding the reader, but are insufficient to power operation of any transponders residing in the surrounding space.
The transponder detection circuit consists of hardware which monitors the level of a transponder detection parameter embodied in the analog data of the ring signals. When the transponder detection circuit determines that the transponder detection parameter has passed a threshold level due to the presence of a transponder in the surrounding space, the transponder detection circuit switches the excitation signal generator circuit from the reduced power state to an increased power state and generation of the ring signals is terminated. The excitation signal generator circuit draws increased electrical current from the power source in the increased power state to generate an excitation signal which is sufficient to power the transponder. The excitation signal is transmitted by the reader and received by the transponder to power the transponder circuitry. The transponder circuitry in turn generates a transponder data signal containing digital data, which is transmitted to the reader. The reader reads the digital data contained in the transponder data signal and the excitation signal generator circuit switches back to the reduced power state, resuming generation of the ring signals while terminating generation of the excitation signal. It is apparent that the duty cycle of the excitation signal generator circuit is significantly lower when operating in the reduced power state than when operating in the increased power state. As a result, the life of the power source is greatly extended and more electrical power is available to the other operations of the reader.
As such, the present invention recognizes a need for a reader which integrates many reader functionalities, including reader power conservation and other analog and digital data acquisition and processing, into a reader microcontroller to realize economies of size and/or cost while maintaining or enhancing reader performance. Accordingly, it is generally an object of the present invention to integrate a plurality of reader functionalities into a reader microcontroller. It is generally another object of the present invention to realize economies of size and/or cost over prior art reader designs while maintaining or enhancing reader performance. More particularly, it is an object of the present invention to integrate certain power conservation functionalities of the reader into a reader microcontroller. It is a further object of the present invention to integrate other analog and digital data acquisition and processing functionalities of the reader into a reader microcontroller. It is another object of the present invention to eliminate the external multi-stage band pass amplifier altogether or to at least reduce the number of stages of the external multi-stage band pass amplifier in the circuitry of the reader. It is yet another object of the present invention to substitute lower cost and simpler electronics for the external multi-stage band pass amplifier in the circuitry of the reader, which produce suitable input signals for processing by an integrated microcontroller of the reader. It is a still further object of the present invention to readily accommodate a range of carrier frequencies, data rates, and modulation types for signals received by the reader. These objects and others are accomplished in accordance with the invention described hereafter.